Microporous support medium

ABSTRACT

THE MICROPOROUS SUPPORT MEDIUM COMPRISES A BACKING ELEMENT MADE FROM A SUITABLE MATERIAL SUCH AS PLASTIC, WITH THE BACKING ELEMENT HAVING ON ONE SIDE THEREOF A HOMOGENEOUS RELATIVELY BRITTLE OR FRAGILE CELLULOSE ACETATE FILM WHICH ADHERES THERETO AND HAS AN ACETYL VALUE OF 20% TO 44% INCLUSIVE.

P 30, 1974 T. L. GOLIAS 3,808,118

MICROPOROUS SUPPORT MEDIUM Filed July 1, 1971 FIG.4

INVENTOR. TIPTON sou/x5 BY' 40 W A oRmiYs UnitedStates Patent Office3,808,l l8 Patented Apr. 30, 1974 US. Cl. 204-499 8 Claims ABSTRACT OFTHE DISCLOSURE The microporous support medium comprises a backingelement made from a suitable material such as plastic, with the backingelement having on one side thereof a homogeneous relatively brittle orfragile cellulose acetate film which adheres thereto and has an acetylvalue of 20% to 44% inclusive.

This application is a continuation-in-part of my copending applicationSer. No. 806,818 filed Mar. 13, 1969', now abandoned.

BACKGROUND OF THE INVENTION-FIELD The microporous support medium of thepresent invention may be used in the field of zone electrophoresis andwith other separation techniques including the field of thin layerchromatography. Zone electrophoresis is the science of moving chargedparticles in an electric field through a solid or semi-solid medium. Thetechnique is most commonly used in medical research and medicallaboratories for analyzing various blood proteins. Many types of supportmedia have been used for zone electrophoresis including filter paper,agar gel, starch gel, acrylamide gel, silica gel, cellulose acetatepowder, cellulose powder, and cellulose acetate membrane. Many of theprior art support media have been coated onto glass or plastic sheets toadd extra resiliency to the support media and to make them easier tohandle.

SUMMARY OF THE INVENTION In accordance with the present invention aspecial type of cellulose acetate coated plastic material and the methodof making same is disclosed. 'The support medium'is a hypergel celluloseacetate having an acetyl value of 20% to 44% supported in its entiretyby a backing element, as an example, by a-relatively rigid plastic base.The preferred range for the acetyl value is 20% to 37%, although asindicated acetyl values up to as high as 44% are within the broad scopeof my invention. The support medium when compared to prior artstructures offers greatly improved resolution and exhibits'easierhandling characteristics. Separation time is approximately 20% less thanthat of commercially available cellulose acetate membranes and at leasta 20% improved resolution is achieved under the same conditions. Thesupport medium has excellent handling characteristics and thetechnicians time required per sample is reduced by approximately 50%.

This invention consists of a cellulose acetate coated backing elementwhich uses one or more cellulose acetates having an average acetyl valueof 20% to 44%. As already noted, the prefererd range for the acetylvalue is 20% to 37%. The cellulose acetate is formed on the plastic orother material by a process described later. The advantage of .this typeof cellulose acetate product is that it absorbs more water and reaches ahigher gel state than previously commercially available materials orproducts. The present invention yields both higher resolution and fasterseparations, both of which are very important in electrophoresis. Thecellulose acetate layer is neither a powder nor a membrane, but is at astage between the two. The cellulose acetate film or layer ismicroporous to a high degree and completely homogeneous, but verydelicate. The film or layer is easily scraped off the plastic backingelement thus distinguishing it from a cellulose acetate membrane coatedplastic product like that sold by Millipore Corporation under thetrademark Phoroslide where it is ditficult to scrape or to remove thecellulose acetate from the plastic base. In the present invention thecellulose acetate layer is attached or bonded to the plastic supportduring the casting and forming operations without requiring bondingagents such as an adhesive which is required in Millipore support mediasold under the trademark Phoroslide.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF A PREFERRED EMBODIMENTThe microporous support medium or cellulose acetate plate is designatedby the numeral 10 in FIG. 1 and consists of two layers. The backingelement 12 forms one of the layers while the other layer 14 is composedof a low acetyl value cellulose acetate film. The backing element 12 maybe made from rigid, semi-rigid, resilient or yieldable materials such asplastic, glass or aluminum. The cellulose acetate layer 14 is applied bya casting operation to one side of the backing element 12 by a method tobe subsequently described and forms a relatively fragile or delicatehomogeneous cellulose acetate film which adheres directly to the backingelement 12. The cellulose acetate is applied to the backing element 12in a solution and must have an average acetyl value of 20% to 44%. Ithas been found that the average acetyl value of the cellulose acetatewithin the range of 20% to 37% inclusive provides excellent propertiesand performance results. As previously noted, cellulose acetate with anacetyl value up to as high as 44% may be employed. I have found thatwith extended drying the higher acetyl value cellulose acetates willbond satisfactorily to the backing element.

The following examples illustrate typical procedures A cellulose acetatesolution is prepared by dissolving seven parts by weight of a 32% acetylvalue cellulose acetate (Eastman 320) in 15 parts dioxane, 15 partsacetone, 38 parts ethyleneglycolmonoethyl ether and 25 parts ethyleneglycol. The cellulose acetate resin utilized is dissolved in the activesolvents consisting of acetone and dioxane and is suspended in thenon-solvents consisting of the remaining specified ingredients. Theresulting mix is blended for approximately 5 minutes at a low speed andremains in such state indefinitely and at least for a 60- minute periodprior to casting.

EXAMPLE 2 A cellulose acetate solution is prepared by dissolving 3.7% byweight of a cellulose acetate (East-man 320) having an acetyl value of32% in active solvents including 13.3% by weight of acetone and 15.9% ofdioxane.

Such solution is allowed to set at room temperature for 12 hours. Ahigher acetyl value cellulose of 39.4% (Eastman 394.60) is also used bytaking 43% by weight and mixing same with the inactive solventsincluding 23.5% by weight of ethylene glycol, 39.09% by weight ofethylene glycol monoethyl ether and .3% by Weight of Triton X100. Theresulting mix is shaken by hand for 15 seconds and then poured into theactive solvents containing the 32% acetyl value cellulose acetate. Theresulting solution, having an average acetyl value of less than 37%, isthen blended for minutes at a low speed. The solution remains in theresulting state indefinitely and must set at least 60 minutes prior touse.

APPARATUS AND METHOD The apparatus and equipment utilized in the presentinvention is illustrated in FIGS. 2-4 inclusive and includes a table orbase 16 having a horizontally extending support or platform 18. A frame20 is supported by the base 16 and includes a pair of transverselyspaced horizontally extending rods 22, joined at their ends by crossbraces 23, and vertical supporting struts 24, as illustrated in FIG. 3.The frame 20 forms a support for a plastic cover 26 which is adapted toclose the sides and top of the frame 20, with the ends of the frameremaining open, and thereby form a tunnel or enclosure 28. The cover 26is normally in a folded or raised position as is shown in FIG. 3, exceptduring the forming operation as will be subsequently described.

A glass plate 30 is carried by the platform 18. The plate 30 has alength and width approximating the size of the platform 18. A draintrough 32 is connected to the platform 18 to permit excess solvents andwater to run off from the glass plate 30. A high volume fan 34 islocated near one end of the platform 18 directly opposite the entranceto tunnel 28. A roll 36 of plastic material is mounted on a support 38beneath the platform 18.

In operation, the glass plate 30 is washed and cleaned prior to use. Anelongated strip of plastic material from roll 32 is removed and isdisposed over the length of the glass plate 30 and forms the backingelement 12. It has been found that plastic sold under the trademarkMylar produces an excellent backing element. The backing element 12 maybe of any suitable length or Width. In actual operation a sheet or striphaving a width of 24", a length of 204" and a thickness of .010" isused. After the plastic backing element 12 is rolled onto the glassplate 30, a suflicient quantity of water is poured over the entirelength of the plastic strip or backing element 12 to remove impuritiesand dirt therefrom. Excess water is then removed from the plasticbacking element 12 and is then wiped dry along the upper surface and theside edges thereof.

A conventional blade spreader 40 extending the width of the plasticbacking element 12 is placed at one end thereof and a sufficientquantity of the cellulose acetate solution is placed therein. Thespreader 40 is set as an example at .032. The spreader 40 is thenrapidly pulled the entire length of the plastic backing element 14 byone workman to form a very thin film 14 of uniform thickness on thebacking element 12. A second person turns on the fan 34 when thespreader 40 is approximately 4 feet away and then lowers the curtain 26as soon as possible in order to form the enclosure or tunnel 28. The fan34 forces a flow of air through the tunnel 28 across the celluloseacetate solution at a flow of approximately 500 to 2,000 cubic feet perminute. The blade spreader 40 is moved at the rate of 2 to 5 ft./second. As a result thereof the air flow removes certain of the solventsand the acetate is formed in a period of time from five to 25 minutes,depending on the solution utilized.

After the cellulose acetate film 14 is formed on the backing element 12,the resulting product is cut into Water soluble material, especially thesolvents which may remain; The sheets are then hung without support andallowed to air dry at room temperature. Thereafter the sheets areexamined when dry, placed in uniform stacks and are then cut to thedesired shapes.

There are several factors which aid in obtaining a good bond between thecellulose acetate film 14 and the backing element 12. The celluloseacetate must be formed very quickly. This is accomplished by forcing airrapidly over the spreaded mix surface at volumes up to 2,000 cu. ft. perminute. When a plastic material has been selected as the backingmaterial rather than glass, aluminum, etc. it is also very beneficial toinclude a mild solvent such as dioxane in the cellulose acetate mix.

The cellulose acetate film 14 may be of any uniform thickness. Theproduct 10 having a cellulose acetate film with a thickness ofapproximately .006" has produced excellent results. The resulting film14 is homogeneous, relatively brittle and very delicate and is supportedentirely by the backing element 12.

What I claim as my invention is:

1. A microporous support medium for use in the fields of zoneelectrophoresis, thin layer chromatography and like separationtechniques comprising a relatively rigid backing element of a uniformthickness of approximately .010" having on one side thereof ahomogeneous microporous cellulose acetate relatively brittle film of auniform thickness of approximately .006" having an average acetyl valuein the range of 20% to 37% inclusive adhering directly thereto andsupported thereby.

2. The microporous support medium of claim 1, wherein said backingelement is made from a plastic material.

3. The microporous support medium of claim 1, wherein said backingelement is made from glass.

4. The microporous support medium of claim 1, wherein said backingelement is made from aluminum.

5. The microporous support medium of claim 1, wherein said celluloseacetate is a hypergel cellulose acetate in a stage between a powder anda membrane and is capable of being readily scraped off said backingelement, said cellulose acetate being adhered to said backing element bybeing cast directly thereto without bonding agents or adhesives.

6. A microporous support medium for use in the fields of zoneelectrophoresis, thin layer chromatography and like separationtechniques comprising a backing element of uniform thickness having onone side thereof a homogeneous microporous cellulose acetate relativelybrittle film of uniform thickness having an average acetyl value in therange of 20% to 44% inclusive adhering directly thereto and supportedthereby.

7. The microporous support medium of claim 6, wherein said celluloseacetate is a hypergel cellulose acetate in a stage between a powder anda membrane and is capable of being readily scraped off said backingelement.

8. The microporous support medium of claim 6, wherein said celluloseacetate is adhered to said backing element by being cast directlythereto without bonding agents or i I adhesives. 7

References Cited UNITED STATES PATENTS 3,378,481 4/1968 Saravis et al.204299 3,479,265 11/1969 Elevitch 204-180 G 3,482,943 12/1969 Csizmas etal. 204-299X 3,554,894 1/1971 Zemel 204299 3,594,263 7/1971 Dwyer et al.204-299X 3,635,808 1/19'72 Elevitch 204-180 G 3,691,054 9/1972 shorterlengths or sheets. The sheets are then placed in 1 Canley 204-299 JOHNH. MACK, Primary Examiner A. c. PRESCOTT, Assistant Examiner US. 01.X.R. 204-- 0, 180 s; 161-160; 106196

